The present invention relates to a liquid fuel cell employing a liquid fuel.
In general, fuel cells are classified into gas fuel cells and liquid fuel cells in accordance with whether a fuel supplied to its anode is a gas such as hydrogen or a liquid such as methanol. An oxidizer, which may be a gas or liquid, is supplied to a cathode of the gas or liquid fuel cell. The cathode or anode supplied with a gas as the oxidizer or fuel may be called "gas electrode".
An electrode of carbon powders solidified with a binder has been well known, as disclosed in Japanese Patent Publication No. 17692/70, which is high in chemical stability (that is, high in resistance to both acid and alkaline solutions), small in weight, and high in cell performance. For fabricating the disclosed carbon electrodes, however, a complicated step must be taken which comprises a step of making large secondary particles from fine carbon powders through bridging or aggregation of the powders. The secondary particles are molded under pressure. Further, it has been generally considered that it is advantageous to employ fine carbon powders, (for example, carbon powders having passed through a 500 Tyler mesh) since a large specific or effective surface area is obtained in the electrode and the cell performance is thereby improved. British Patent No. 136,1741 has proposed a gas electrode which is made of press-molded carbon powders of 5-100 .mu.m and has the pore sizes of 0.5-20 .mu.m and a porosity of 5-50% for providing a large specific surface area.
However, the present inventors' experiments have revealed that when fine carbon powders are used for an anode of a liquid fuel cell in which a gas such as CO.sub.2 is generated at the anode as the product of an electrode or cell reaction, there is a problem that the fine carbon powders prevent the reaction gas from escaping to the outside of the anode and therefore the supply of the liquid fuel to the cell through the anode becomes incomplete, thereby deteriorating the cell performance.
The use of relatively larger carbon powders for a gas electrode has been disclosed in U.S. Pat. No. 3,423,247. This patent shows a non-homogeneous two-layer electrode structure which includes a gas-permeable and electrolyte-repellant layer zone of larger carbon powders of 147-74 .mu.m (-65+100 Tyler mesh) at the gas supply side and an electrolyte-permeable layer zone of smaller carbon powders not larger than 208 .mu.m (-200 Tyler mesh) at the electrolyte side. The electrode is fabricated through a press-molding and heating process. The electrolyte-repellant zone has the pore sizes in the range of 1-20 .mu.m and the electrolyte-permeable zone has the pore sizes in the range of 0.1-1 .mu.m. The electrolyte-permeable zone may include three layers having a first layer with carbon powders not larger than 43 .mu.m (-325 Tyler mesh), a second layer with carbon powders of 74-43 .mu.m (-200+325 Tyler mesh) and a third layer with carbon powders of 208-74 .mu.m (-65+200 Tyler mesh). U.S. Pat. No. 3,423,247 suggests the use of such a gas electrode to an anode supplied with a gas fuel as well as a cathode supplied with an oxidizer. However, such a gas electrode, too, has the above-mentioned problem associated with the generation of a reaction gas when it is applied to an anode of a liquid fuel cell.